Direct Electrical Current Used to Preferentially Inhibit Pain-Transmitting Neurons

Source: Johns Hopkins University School of Medicine

Summary: Using computer models and laboratory rats, researchers have demonstrated that “direct electrical current” can be delivered to nerves preferentially, blocking pain signals while leaving other sensations undisturbed.

Implantable spinal cord stimulators and peripheral nerve stimulators designed to interrupt nerve pain impulses were developed more than 30 years ago, but the devices work by interacting with sensory nerve cells, leading to numbness, tingling and other side effects. Traditionally, direct current or single direction streaming electrical signaling has been considered unsafe for medical devices that deliver electrical stimulation in the body. Using computer models and laboratory rats, researchers from the Johns Hopkins University School of Medicine have demonstrated that “direct electrical current” can be delivered to nerves preferentially, blocking pain signals while leaving other sensations undisturbed. The researchers say the experiments advance the search for improved implantable devices able to treat chronic pain that is due to peripheral nerve injury or disease. The study findings were published in the journal Science Advances.

unidirectional flow of electric charge

Gene Fridman (left) and Yun Guan examine a prototype of a device that delivers direct current safely. Credit: Johns Hopkins Medicine

The research team first devised a computer model to try to predict what happens when researchers use direct current to block the pain signals or inhibit other sensory neurons. In the model, they sent negatively charged direct current to the nerves to weaken their activity. The model showed that the sodium channels 1.6 in the feeling sensory neurons were blocked with 670 microamperes, but the pain neuron’s sodium channels 1.7 were blocked at only 290 microamperes. For comparison, holding a 9-volt battery to the tongue delivers approximately 2,000 microamperes, causing a small shock. This suggested to the researchers that it was theoretically possible to preferentially target one type of neuron over another since the channels could be blocked at different levels of current.

Assoc. Prof. Yun Guan said, “Using direct current, we can inhibit the pain-transmitting neurons at much lower amplitudes than the feeling sensory neurons, allowing us to be preferential in how we target the nerve.”

More Information: Fei Yang et al, “Differential expression of voltage-gated sodium channels in afferent neurons renders selective neural block by ionic direct current”, Science Advances (2018). DOI: 10.1126/sciadv.aaq1438 

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